Fracture Toughness Measurement using a Ring Specimen

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  • リング試験片による破壊靱性値の測定

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A fracture mechanics approach, using fracture toughness(KIC)failure criterion, is the most appropriate method for brittle materials such as posterior composite resins.Recently, one of us developed a new method for determination of the KIC value using a specimen in the shape of a ring.In this study, we discussed the advantages of the ring specimen and measured the KIC value of three commercial posterior composite resins(Clearfil photo posterior, P-50 and Occlusin).It is easy to introduce a fatigue-precrack in the ring specimen used in this study and to control the crack length with a fatigue testing machine.The ring specimen demonstrates a constant stress intensity factor over a significant range 0.58≦(a+Ri)/Ro≦0.76, so that the exact measurement of the crack length is unnecessary.The KIC values of OCC(1.87±0.07MPam1/2)showed significantly higher values than CPP(1.52±0.03MPam1/2)and P-50(0.88±0.05MPam1/2).The average coefficient of variance was 2.7%.In conclusion, the ring specimen is a reliable, accurate and reproducible means of measuring the KIC value.

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